For example, a pressurized water reactor in a nuclear power plant uses light water as nuclear reactor coolant and neutron moderator, makes the light water be high-temperature and high-pressure water not boiling over through the entirety of a reactor internal, generates steam through heat exchange by sending the high-temperature and high-pressure water to a steam generator, and generates electricity by sending the steam to a turbine generator.
In the pressurized water reactor, a reactor internal is provided in a nuclear reactor vessel and the reactor internal is constituted of a plurality of fuel assemblies. In other words, in the nuclear reactor vessel, a core barrel having a cylindrical shape is arranged with a predetermined gap from the inner wall surface thereof. The upper portion of the core barrel is supported to be suspended from the nuclear reactor vessel and a plurality of fuel assemblies are arranged in the core barrel. An example of such a nuclear reactor vessel is disclosed in Patent Literature 1 described below.